Independent aircraft landing monitor system

ABSTRACT

An aircraft landing monitor which is independent of ground-based guidance systems and which includes an antenna comprising an elongated housing pivotally mounted about a vertical axis for horizontal movement in the forward portion of an aircraft. The housing supports an edge-slotted waveguide array which is mounted in an elongated horn reflector to thereby direct an antenna radiation pattern forward of the aircraft which is narrower in the azimuth than in the elevation plane. A motor oscillates the antenna housing about the vertical axis to sweep over an azimuth angle sufficient for airport runway detection during a glideslope approach to the runway by the aircraft. Radar transmitter and receiver circuits transmit and receive pulse radar signals via the antenna for radar detection of the runway. A radarscope mounted in the cockpit control panel is responsive to the radar transmitter and receiver for visually displaying an approaching airport runway in real-world linear perspective.

United States Patent 1 Bechtel Feb. 13, 1973 INDEPENDENT AIRCRAFTLANDING MONITOR SYSTEM [75] Inventor: Bartow Bechtel, Richardson, Tex.[73] Assignee: Texas Instruments Incorporated,

Dallas, Tex.

[22] Filed: July 15, 1970 [21] Appl. No.: 54,979

[52 U.S. Cl ..343/l1 R, 343/5 LS, 343/5 SC [51] I nt.Cl ..G01s7/12, GOls7/16, GOls 9/06 [58] Field of Search.343/5 R, 5 LS, 5 SC, 7 A, 7 TA,343/73, 11 R, 13 R, 18 B, 18 C, 705, 756, 762, 786

[56] References Cited UNITED STATES PATENTS 3,177,484 4/1965 Case et al.l ..343/5 LS R25,756 4/1965 Balding ...343/5 LS 2,871,470 1/1959Stephens0n..... ...343/5 LS 1 3,146,449 8/1964 Serge et al.......343/756 3,110,022 11/1963 Gebhardt.... .....343/5 R 2,611,126 9/1952lrving ...-343/11 R 2,426,218 8/1947 Hopgood ...343/5 LS 3,181,1534/1965 Cella ...343/5 LS 3,309,659 3/1967 Balding ..343/5 R PrimaryExaminerStephcn C. Bentley Attorney.lames 0. Dixon, Andrew M. Hassell,Harold Levine and Rene E. Grossman [57] ABSTRACT An aircraft landingmonitor which is independent of ground-based guidance systems and whichincludes an antenna comprising an elongated housing pivotally mountedabout a vertical axis for horizontal movement in the forward portion ofan aircraft. The housing supports an edge-slotted waveguide array whichis mounted in an elongated horn reflector to thereby direct an antennaradiation pattern forward of the aircraft which is narrower in theazimuth than in the elevation plane. A motor oscillates the antennahousing about the vertical axis to sweep over an azimuth anglesufficient for airport runway detection during a glideslope approach tothe runway by the aircraft. Radar transmitter and receiver circuitstransmit and receive pulse radar signals via the antenna for radardetection of the runway. A radarscope mounted in the cockpit controlpanel is responsive to the radar transmitter and receiver for visuallydisplaying an approaching airport runway in real-world linearperspective.

22 Claims, 22 Drawing Figures SYNCHRO I 52 I 42 I TRANSMITTER I 90 I 6554 F RANGE CONTR L a x l 56 l :l TRACKER MODE SwlTgH l ON-OFF ISYNCHRONIZER I RECEIVER I SWITCH I GLIDESLOPE I i l COMPUTER II WEEPENERATOR UNIT 2 DISPLAY ---64---- vI-:RT. e- 7o ALT. SWEEP I l INPuTREAL'WORLD, SWEEP I I VERT. BIHORZ.

l SWEEP CKT$- SELECTION l I DEFLECTION DVST l PMT. I CIRCUITS IHORZ' IAMPLIFIERS I I ISWEEP I I PPl BI B 72\\ POWER 1 8O 84 SWEEP CKTS.SUPPLIES I I I so we I wg E Fgooo vIIw u UN sc EN OUTPUT UNBLANK aSUPPLY SUPPLY SUPPLY l I ANT P0s| 0 CONTROL INTENSITY I s [I I IDEMODULATOR CKTS. I COMPENSATION I A T 56 82 as T as L- I IUNBLANK]VIDEO 8 MEMORY I INTENSITY a. ERASE I UNBLANK VIDEO I AMPLIFIERS REC.GAIN GEN. K I CONTROLS 74 RECGAIN PATENTED FEB I 31973 SHEET 03 [1F 13PATENTED FEB l 3 I373 SHEET cu [1F 13 PATENTEU 31375 3.716.860

sum 09 [1F 13 FIG. I3

HEADLINE PATENTED FEB] 3191a sum 1 1 0F 13 ON I . N6 M959 Qua/Em mkm sum

PATENTEUFEB 1 3121s Own H mmk Own tronic guidance equipment to enablethe pilot to progressively monitor the final aircraft approach,touchdown and rollout. Specifically, the need has arisen for an onboardindependent landing monitor which provides the pilot with positiveassurance that the aircraft localizer approach is valid, that theaircrafts true position is relative to the runway center line andthreshold is satisfactory and that the airport runway is clear ofobstructions. Such an independent landing monitor is particularlydesirable during blind or low visibility aircraft .takeoffs or landings,and during landings at airports which are unequipped or underequippedwith navigational aids.

Radar systems have previously been utilized onboard aircraft for suchuses as terrain and aircraft avoidance. However, previously developedaircraft radar systems have not been generally useful as independentlanding monitors, due to antenna resolution and display deficiencies.Display limitations of such prior radar systems have made meaningfullanding decisions impossible, such as identifying runway and taxiwaysand accurately determining the aircraft angle to the runway center line.For instance, a conventional planned position in- 4 dicator (PPI) radardisplay provides accurate range and angle presentation of an approachingrunway, but

this display presents a birds eye" view of the runway which gives anaircraft pilot a false sense of altitude, no sense of urgency forlanding and makes fora difficult transition to a visual inspection ofthe approaching runway. Additionally, the .conventional B-scope anddelayed B-scope presentation, wherein range is plotted against anindependent variable scan-angle, provides adequate identification ofrunway patterns at long range where the angular distortion is minimal,but provides extreme distortion of the runway at the minimum decisionaltitude during an aircraft landing, thereby preventing the pilot fromaccurately identifying the runway and taxiways andmaking it impossibleto accurately determine the aircraft angle to the runway center line.

In accordance with the present invention, a short range, high-resolutionmapping radar system is located onboard an aircraft and is independentof groundbased electronic equipment to monitor runway alignment and thelike during approach, touchdown and rollout phases of aircraft landing.The present system utilizes a high resolution antenna system incombination with a visual radar display which presents a realworld"display of the approaching runway to the pilot on a one-to-onecorrespondence to real-world perspective. The pilot may then accuratelyidentify the runway threshold, accurately determine the angle to centerof the runway, measure lateral offset and'make a smooth transition tovisual runway information.

-ble in an aircraft and having a radiation pattern suffi' cient in theelevation for detection of an airport runway when the aircraft is onfinal approach. The antenna also has a narrow radiation pattern in theazimuth to provide high resolution for runway detection. A motor sweepsthe antenna over an angle in the azimuth which is sufficient fordetection of an airport runway. A radar transmitter and receivertransmit and receive pulsed radar signals through the antenna. A displayis responsive to the radar receiver for displaying a visual indicationof the approaching runway to the aircraft pilot.

In accordance with another aspect of the invention, an antenna ismounted in an aircraft and is operable to transmit and to receive radarsignals for detection of an airport runway during a glideslope approach.Radar transmitting and receiving circuitry transmits and receives radarsignals via the antenna. A display scope visually presents a display ofthe approaching aircraft runway which corresponds to the real-worldperspective view of the runway from the aircraft.

In accordance with yet another aspect of the invention, an aircraftlanding monitor includes an antenna having an elongated housingpivotally mounted for horizontal movement in the forward portion of theaircraft. The housing supports an edge-slotted waveguide array mountedin an elongated horn for directing an antenna radiation pattern narrowerin the azimuth than in the elevation plane. A motor is mounted tooscillate the housing to thereby sweep over an azimuth angle sufficientfor airport runway detection during glideslope approach by the aircraft.Radar transmitter and receiver circuits transmit and receive pulsedradar signals via the antenna, and a radarscope is responsive to thereceiver circuit for visually displaying an approaching airport runwayin real-world linear perspective.

For a more complete understanding of the invention and for furtherobjects and advantages thereof, reference may now be made to thefollowing description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a somewhat diagrammatic illustration of the antenna radiationpattern of the invention in the elevation plane during glideslopeapproach;

FIG. 2 is a somewhat diagrammatic illustration of the azimuth sweepofthe antenna radiation pattern of the present system;

FIG. 3 is' a somewhat diagrammatic illustration of the installation ofthepresent landing monitor radar system in the nose of an aircraft;

FIG. 4 is a block diagram of the present landing monitor system; a

FIG. 5 is a central sectional view taken of the antenna of the presentsystem;

FIG. 6 is a top view, partially broken away, of the antenna shown inFIG. 5;

FIG. is a front view, partially broken away, of the antenna shown inFIG. 5;

FIG. 8 is a perspective view of a portioniof the slotted waveguideassembly utilized in the antenna shown in FIG. 5; v

FIG. 9 is a block diagram of the antenna sweep control circuitry of theinvention;

FIG. 10 is a block diagram of the radar receiver utilized in the presentsystem;

FIG. 11 is a block diagram of the radar transmitter utilized in thepresent system;

FIG. 12 is a block diagram of the sweep generation circuitry utilized tocontrol the radar display of the present invention;

FIGS. 13 and 14 are diagrammatic illustrations of the relationshipsbetween the range and altitude of the aircraft in the display of therunway during glideslope approach;

FIGS. 15 and 16 are diagrams illustrating aspects of the theory ofoperation of the present radarscope dis- P y;

FIG. 17 is a graph illustrating the relationship between elevationangle, range and altitude according to the present display system;

FIG. 18 is a graphical representation of the nonlinear voltages utilizedto control the vertical sweep of the present radarscope display;

FIGS. 19a-d are somewhat idealized illustrations of the presentradarscope display during approach to an airport runway;

FIG. 20 is a detailed schematic of the nonlinear voltage generators inthe sweep generator circuit of the invention;

FIG. 21 is a detailed schematic of the delay circuitry for generation ofthe unblank signal for use in the sweep generator of the invention; and

FIG. 22 is the detailed schematic of the storage, clamping and summingcircuits utilized in the sweep generator circuit of the invention.

Referring to the FIGURES, FIGS. 1 and 2 somewhat craft 10 with anelevational antenna beam width 14 of about 17. As shown in FIG. 2, theazimuth antenna beam width 16 is approximately 04 and is continuouslyswept over an azimuth sweep angle 18 of approximately 30. The sweptantenna beam configuration provided by the system enables highresolution radar mapping of the approaching runway 12 during landing ofthe aircraft l0. Radar reflection signals from the runway 12 and thegrass and terrain surrounding the runway are received by radar receivingcircuitry in the nose of the aircraft l0 and the runway 12 is displayedin real-world perspective to the pilot.

In the preferred embodiment of the invention, a maximum range of aboutfive miles, with a range of about two miles for initial runwayacquisition, is afforded to the landing monitor radar system. Aircraftl0, landing with-typical glide-slope angles of from 2.5 to 3.0, willthus be about 2,600 feet from the end of the runway 12 at an altitude of200 feet and about 1,200 feet from the runway 12 at a decision altitudeof 100 feet.

FIG. 3 is a cutout view of the nose portion of a conventional aircraftto illustrate the basic components of the present landing monitorsystem. A mechanically swept antenna 20 is located in the nose of theaircraft and comprises an elongated edge-slotted waveguide array 22which is reciprocated about a vertical axis 24. As may be seen from FIG.2, the antenna 20 is periodically swept 15 on either side of thelongitudinal axis of the aircraft 10 to provide the 30 sweep angle 18.In the preferred embodiment, antenna 20 is swept at a rate of 2.5 cyclesper second.

Pulsed radar signals are transmitted via the antenna 20 through suitablewaveguide connections 26 which extend from a transmitter-receiverhousing 28. The return radar signals are received by receiver circuitrywithin the housing 28. Sweep generator circuitry is contained within ahousing 30 and provides electrical signals via leads 32 to a displaymonitor radarscope 34 mounted in the instrument panel of the aircraft.Display monitor 34 is preferably of the direct view storage tube typeand provides a display surface 36 wherein the pilot may receive areal-world perspective indication of the upcoming runway 12. Displaymonitor 34 includes various adjustment and select knobs to providealternative conventional B sweep and PPI display sweep modes if desired.Power supply circuitry for the system is contained within a housing 38.

The present system provides a practical independent landing monitorsystem for use on large passenger capability jumbo jet aircraft. Thepresent high resolution radar system permits visual assessment to thepilot of the aircrafts alignment with the runway center line during thefinal phase of approach, even in the event of inclement weather such asrain, snow or fog which provides zero-zero visibility.

FIG. 4 is a block diagram of the basic independent landing monitorsystem. The antenna 20 is oscillated about a rotary joint 40 by a torquemotor 42. A synchro or control transformer 44 senses the instantaneousposition of the antenna 20 and supplies a signal via a lead 46 to anantenna position demodulator circuit 48. The demodulator 48 generates aslowly varying DC voltage which is supplied to an output control circuit50 which serves to operate upon the duty cycle of voltage pulsessupplied to the torque motor 42 in order to maintain the desiredoscillation of the antenna 20. For instance, if the oscillation of theantenna 20 begins to decrease in magnitude, the output control circuit50 drives the torque motor 42 to increase the angle of antennaoscillation.

The antenna 20 is connected through a circulator 52 to a radartransmitter 54 and a radar receiver 56. Circulator 52 operates as aduplexing circuit in order to couple the antenna 20 with either thetransmitter 54 or the receiver 56. A synchronizer circuit 58 isconnected for control of the transmitter 54, and comprises a clockcircuit (not shown) containing an RC oscillator which establishes thePRF for the system. A PMT monostable multivibrator circuit (not shown)is triggered by the clock to set the pulse of the premaster trigger(PMT) of the system. The PMT is fed through buffer circuits to variousportions of the system, as will be described later in greater detail.

The PMT is fed from the transmitter 54 to the sweep generator unit andspecifically to real-world sweep circuits 60 and PPI and B sweepcircuits 62. An altitude input signal representative of the altitude ofthe aircraft is also fed into the real-world sweep circuit, and outputsare generated for application to sweep selection circuits 64. The sweepselection circuits 64 are controlled by mode switches in a control box66. When the real-world mode is selected, the real-world sweep circuits60 drive vertical and horizontal deflection amplifiers 68 to provide areal-world perspective display on the direct view storage tube.(DVST)70. When the PPI mode is selected at the control box 66, the PPI sweepcircuits 62 drive the vertical and horizontal deflection amplifiers 68to provide a plan position indicator display in the well known manner atthe DVST 70. When the B sweep selection is made at control box 66, the Bsweep circuit 62 operates to drive the vertical and horizontaldeflection amplifiers 68 to provide a conventional B sweep indication atthe DVST 70. Power is provided to the various portions of the systemfrom suitable power supplies 72.

The receiver 56 is of the quasilog type and generates signals via leads74 which are applied to video amplifiers 76. An unblank and intensitycompensation circuit 78 supplies an unblank signal to the amplifier 76.Amplifier 76 supplies the amplified video and unblanking signals to thewrite gun supply 80 to control the intensity of the electron writingbeam of the DVST 70. The intensity control 82, mounted on the frontpanel of the display, controls the gain of the unblanking amplifier 76,which in turn controls the brightness of the video information writtenon the DVST. The memory control 82, also mounted on the front panel ofthe display, is used to control the persistence (or storage time) of thedisplay. The memory control operates upon the erase generator circuitry86 and causes it to supply a variable duty cycle pulse train to thebacking electrode of the DVST 70. This in turn controls the amount ofinformation erased from the storage surface of the DVST. The erasegenerator 86 also supplies a pulse, coincident with the erase pulse, toa dunk tube (not shown) which drops the view screen supply 88 voltage toa very low level for the duration of the erase pulse. This eliminateslight bursts that would otherwise occur for the erase pulse duration.The flood gun supply 84 provides the necessary voltages to the DVST suchthat flooding beam" is properly ,collimated. The receiver gain controlsupplies a signal to the receiver 56 to vary the amplitude of the radarvideo which is supplied to the display.

The DVST 70 is of conventional design, and a suitable tube for use withthe invention has a writing speed of 450,000 inches per microsecond andis manufactured and sold by Westinghouse Corporation. Basi-v cally, thefloodgun of the DVST illuminates a grid which is selectively charged bythe write gun of the tube. The tube thus has persistence which isdetermined by the duty cycle of the erase generator which is pulsed toerase the image on the DVST. The unblanking circuits of the systeminhibit the display during the retrace time of the sweeps.

The unblanking circuits enable the display to write video and symbologyon the DVST during the active portion of the sweeps. The intensitycompensation circuits 78 provide a compensation signal superimposed onthe unblanking pedestal pulse to correct for the differences in sweepspeed (inches/usec) and the density of radar returns at different areason the display screen. The use of the DVST 70 is advantageous in thesystem as'the tube supplies an integrating quality. Therefore, weakpulses received by the system tend to be integrated due to the fact thata large number of hits (radar returns) strike the same resolution cellon the screen of the DVST.

A range tracker system 90 receives the PMT from synchronizer 58, theradar video from receiver 56, and the antenna position signal fromdemodulator 48. The range tracker system 90 generates indications of therange of the aircraft to runway touchdown. In the preferred embodiment,a plurality of passive reflectors are arrangedadjacent the airportrunway in a predetermined pseudorandom coded configuration, and thetracker system 90 detects radar reflections from the reflectors toaccurately determine the aircraft range to the reflectors. This rangetracker system 90 is described in detail in the copending patentapplication Ser. No. 055,165, filed July 15, 1970, and entitled RangeTracking System for Use In An Independent Aircraft Landing Monitor."

The range information generated by tracker 90 is fed to the amplifiers76 for display to the pilot on the DVST 70. The range information isalso fed to a glideslope computer 92 which detects the relativeamplitudes of radar signals reflected from predetermined reflectorsadjacent the runway to generate indications of the position of theaircraft relative to the runway glideslope. The indications are fed toamplifiers 76. For a more detailed description of the glideslopecomputer, reference is made to the copending patent application Ser. No.055,164, filed July 15, 1970, and entitled Glideslope Position DetectionSystem for Use With An Independent Aircraft Landing Monitor.

ANTENNA SYSTEM FIGS. 5-7 illustrate the antenna assembly 20. A generallycylindrical member is adapted to be rigidly attached to a radomebulkhead within the nose of an aircraft. A housing 102 is connected tothe cylindrical member 100 and supports the oscillating antennaassembly. A lower housing 104 contains a rotary joint 106 which enablesrotation between a fixed waveguide section 108 and a waveguide section110 which is attached to the oscillating antenna. The waveguide assembly108 is connected to the transmitter and receiving circuitry of thesysterri. The entire waveguide assembly of the system is normallypressurized with Freon-1 I6. A control transformer 111 is connected to atorque motor including a torque rotor'l12 and a torque motor stator andhousing 114. The control transformer lll senses the position of theantenna and supplies signals to the antenna control loop previouslydescribed in order to provide control signals to the torque motor tomaintain the desired oscillation of the antenna.

The output shaft I 16 of the torque motor is mounted in bearings 118 andis fixedly attached toan antenna housing I20 for oscillation thereof. Ashaft 122 is fixed at the upper end of the housing 124 which is boltedonto housing 102. An outer housing 126v is connected to the oscillatableantenna and is mounted in bearings 128 and 130 for relative rotationwith respect to thefixed housing of the antenna system. The lower end ofthe shaft 122 is connected to a generally U-shaped member 132 whichreceives. a center portion of an elongated flexible metal spring 134. Abolt 136 enables the U-shaped member 132 to be tightly clamped about thecenter of the spring 134. As best shown in FIG. 6, the spring 134extends along the length of the antenna housing 120. The ends of thespring 134 are free, but

are slidably received between rollers 140 at one end, and rollers 142 atthe other end thereof. As the antenna housing is oscillated, the spring134 flexes and rotates relative to the rollers 140 and 142. The spring134 stores energy upon rotation of the antenna housing and tends toreturn the housing back to its previous position.

A real housing portion 146 is attached to housing 120 to provide anaerodynamically streamlined configuration to the antenna. A forwardlyfacing radome 148 is also attached to housing 120. Preferably, radome148 is constructed from a material such as fiberglas to enabletransmission of radar signals therethrough.

An antenna reflector horn 150 is disposed along the front length of theantenna and includes a waveguide 152 along the length thereof. Waveguide152 is connected to waveguide 110. A quarter-wave grid type polarizer154 is mounted in the reflector 150 and is preferably comprised of afoam type dielectric material. A backing channel member 156 is connectedto the reflector 150.

As shown in FIG. 6, in operation the antenna is swept about the verticalaxis extending through shaft 122 about a 30 angle, or on either side ofthe headon position of the antenna. The spring 134 assists inmaintaining oscillation of the antenna and the error signals fed fromthe control transformer control circuit back to the torque motor assistsin maintaining the oscillation of the antenna at the predeterminedangle.

In the preferred embodiment of the antenna, the antenna is approximately60 inches long and 7 inches wide. The present antenna is preferablyoperated in the Ka band of 33 to 38 GHz. With a 2.5 dB antenna loss, theantenna gain for the preferred system is approximately 33.5 dB.

The present antenna is of an edge-slotted waveguide array type. Moreparticularly, reference is made to FIG. 8 which illustrates a section ofthe edge-slotted waveguide 152 utilized in the present antenna. Aplurality of slots 160 slope in a first direction, while alternate slots162 cut through the front face of the waveguide slant in an oppositedirection. The slots are regularly cut in the front narrow wall of thewaveguide 152 and are designed to resonate at a frequency which is twicethe waveguide wave length spacing. Thus, at resonance all of the slotsradiate in phase and the beam is oriented normal to the array length. Atresonance the slots 160 and 162 become a pure conductance and add, sincethe slots are in shunt in the transmission line circuit. At the resonantfrequency, the load is thus pure resistive and is equal to the sum ofthe slot conductances.

To properly illuminate the array, power is extracted from the travelingwave as each slot is illuminated. Because of this, the slot conductanceis increased with distance from the feed point of the waveguide, thusresulting in a total conductance much greater than unity andconsequently resulting in a large resistive mismatch at resonance. Forthis reason, the present array is operated slightly above the resonantfrequency. The beam is thus pointed approximately one to two beam widthsaway from broadside of the antenna. Under this condition, a VSWR of lessthan l.2:l is insured. The present antenna of the preferred embodimentwill operate at 178 wavelengths at the Ka-band.

For additional description of the theory of such edgeslotted waveguidearrays, reference is made to Antenna Engineering Handbook, by H. Jasik,196l, Chapter 9, McGraw-Hill.

The quarter wave plate polarizer member 154 converts the horizontalpolarization of the slotted array feed to circular polarization. Thepolarizer 154 is a quarter wave device comprising a plurality ofregularly spaced narrow metallic vanes supported in the low-lossdielectric Eccofoam material. The orientation of the metal vanes are atan angle of 45 with respect to the antenna polarization to therebyconvert the linear polarization to circular polarization. An integratedcancellation ratio (ICR) of 17 dB is readily achievable utilizing thiscircular polarization technique.

Although not shown, in the preferred embodiment of the antenna, thewaveguide 152 is routed in a second path back along the length of theantenna to maintain symmetrical loading thereof. The waveguide and thereflector antenna horn are generally constructed from aluminum andconnected in a rigid configuration. The torque motor chosen for use withthe invention in the preferred embodiment is a brushless DC torque motorwith a permanent magnet rotor and a toroid coil wound stator. The motoris rated fl5 angular motion, continuous at eight watts and a 20ounce-inch peak torque. A high pressure reserve bottle of Freon-l 16 ismounted near the far end of the waveguide and feeds the waveguide withpressurized Freon-l 16 through a preset pressure reducer. A pressuregauge fitting on the bottle allows checking of the reserve supply and asimilar attachment combined with the lead valve is provided at the endof the waveguide adjacent to the load to allow verification of pressurein the waveguide and to enable bleeding of the system after maintenance.

FIG. 9 illustrates in block detail the circuit for control of theoscillatory motion of the antenna 42. The synchro 44 comprises a lineartransformer which generates a modulated 2,000 cycles per second signalto an output demodulator circuit 168. A reference voltage, whichpreferably is the 2,000 cycle per second aircraft supply voltage, is fedto the synchro 44 and to a reference demodulator and offset sum circuit170. Circuit compensates the aircraft supply voltage for changes involtage amplitude and supplies a constant voltage amplitude to amultiplier 172. Circuit 170 thus prevents detection of changes in theaircraft supply voltage amplitude as changes in the antenna position.

The output of the output demodulator 168 is a slowly varying DC signalat the antenna scan rate, which in the preferred embodiment is 2 cyclesper second. The output of the demodulator 168 is thus responsive to theinstantaneous position of the antenna 20. The output of the multiplier172 generates a signal responsive to the antenna position to the 90phase shifter 174 and to the absolute value amplifier 176. The 90 phaseshifter 174 shifts the sinusoidal output from the multiplier 172, suchthat zero crossings thereof are representative of the occurrence ofpeaks of the waveforms. A positive zero crossing detector 178 generatesan electrical indication of the positive amplitude peaks of the antennaposition signal, while a negative zero crossing detector 180 providesindications of the negative voltage peaks of the amplitude positionsignal.

The output of detector 178 is fed to an input of an OR logic 182 andalso to the trigger input of a voltage variable pulse width monostablemultivibrator 184. The output of the detector 180 is also fed throughthe OR logic 182 and also to the trigger input of a voltage variablepulse width monostable multivibrator 186. The multivibrator 184 istriggered upon the occurrence of each positive peak of amplitudeposition signal, while the multivibrator 186 is triggered only upon theoccurrence of negative peaks of the antenna position signal.

The output of the OR logic 182 is fed to a sample and hold amplifier188. The absolute value amplifier 176 rectifi es the position signalfrom the multiplier 172 and gives a positive voltage output indicativeof both the left and right scan peak positions of the antenna. Thisinformation is fed to the sample and hold amplifier 188, which generatesa positive voltage representative of the peak left and right position ofthe antenna only upon the occurrence of a position peak as detected bythe OR logic 182. This voltage is applied to the multivibrators 184 and186. As the multivibrators 184 and 186 are alternatively triggered bydetectors 178 and 180, a monostable multivibrator output pulse isalternatively generated by the multivibrators which is representative ofalternating left and right antenna position peaks.

The pulse width of the multivibrator outputs is dependent upon thedetected position of the antenna. The pulse outputs from themultivibrators are fed to a driver matrix 188, which may comprise atransistor driver or an SCR circuit driver. The pulse outputs are thenapplied to the torque motor 42 in order to control the position of theantenna. One of the pulse outputs drives the motor 42 in a clockwisedirection while the other pulse outputs drive the motor 42 in acounterclockwise direction. If the antenna oscillation begins to slowdown, the pulse width of the outputs from the multivibrators isincreased to increase the drive to the antenna. Conversely, if the peakleft and right positions of the antenna begins to exceed predeterminedposition limits, the width of the pulse outputs from the multivibrators184 and 186 decreases in order to decrease the driving motion to themotor 42.

RADAR RECEIVER FIG. 10 illustrates a block diagram of the radar receiverof the invention. Radar signals received by the antenna are fed throughthe ferrite circulator 52, previously described. A load 200 is attachedto the circulator 52 for use in testing of the receiver. The transmittermagnetron is also connected to the circulator 52. The circulator 52 isoperated as aduplexer to permit the use of a single antenna. The signalsfrom the transmitter are sampled through a coupler 202 and are fedthrough a power monitor circuit 204 to one input of a NAND gate 206 andthe built-in test equipment unit of the system.

The received signals from the antenna are transmitted through thecirculator 52 which may comprise the circulator R-64l-LS manufacturedand sold by Ferrotech, lnc. to a T-R switch 208. Switch 208 maycomprise, for instance, the switch tube MA-3773 manufactured and sold byMicrowave Associates. A keep-alive circuit 210 biases the T-R switch 208so that the switch tube is on the verge of breaking down in order toprovide signal isolation in the known manner. The received signals arefurther fed through a ferrite switch 212 which provides additionalattenuation from the transmit pulse. The ferrite switch may comprise,for instance, the LTW103 switch manufactured and sold by Ferrotech, Inc.The PMT signal is fed through a switch driver 214 in order to controlthe operation of the ferrite switch 212.

The receiver signals are fed through a signal mixer comprising diodes216 and 218 connected at opposite polarity terminals. A resistance 220is connected across the diodes and is also connected to two inputs of aNAND gate 222. A solid state local oscillator 224 comprises a voltagecontrolled oscillator which supplies a 50 MW signal at 1.458 GHz to apower amplifier which increases the power to about one watt. The signalis then fed through a x6 multiplier which preferably will comprise athin-film device. The resulting 250 MW signal at 8.75 GHz is fed througha x4 multiplier to generate the final 10 MW signal at 32.94 GHz 1150MHz. The resulting signal is fed through an isolation circuit 226 formixing with the received signals. The frequency applied to a linearamplifier 228 comprises a 60 MHz intermediate frequency.

The IF signal is amplified in the linear amplifier 228 and a sensitivitytime control (STC) signal is applied to reduce the receiver saturationas the target range' decreases. The STC signal is applied from agenerator 230 which is controlled by the PMT signal of the system. Theamplified signals are applied through a log post amplifier 232 wherein afinal dB gain is applied to the signal. A manual gain adjust control isapplied to the amplifier 232. Amplifier 232 has a linearlogarithmiccharacteristic matched to the indicator dynamic range of the system toinsure the optimum display of radar target information. In the preferredembodiment, the amplifier 232 comprises seven amplification stages allof which operate for low power signals. The stages begin to saturate oneby one as the received signal becomes stronger, in order to give avoltage output which is a linear function of the input power to thesystem.

The output of amplifier 232 is applied to a video detector and amplifier234 which includes an emitter follower output. The detector 234regulates the 60 MHz signal and operates as an envelope detector togenerate a video voltage pulse. A fast time constant (FTC) operation maybe applied at the amplifier 232 at the operator's option. The FTCoperation serves to break up targets with large cross section, such asterminal buildings or residential areas, to prevent the saturation ofthe radar display. The video voltage pulses are applied to the indicatorof the system in a manner to be later described in greater detail.

A power monitor coupler 236 detects the signals transmitted from themagnetron and applies the signals to an AFC mixer comprising diodes 238and 240 connected at opposite polarity terminals. The output from theisolator circuit 226 is also monitored by a coupler 242 and applied tothe AFC mixer. The mixed signal, when the system is correctly operating,should be at the IF frequency and is applied through a limitingamplifier 244 to the AFC circuit 246. The output of the AFC circuit 246is applied to an input of the gate 222. The AFC mixer is also connectedto two inputs of the gate 222.

The AFC circuit 246 is connected through a movable switch arm 248 whichis movable between connection to the local oscillator 224 and connectionto a terminal 250. Terminal 250 is connected to a test load resistor 252which is connected to circuit ground.

The above-described AFC circuit maintains the receiver in frequencysynchronization with the transmitter. When the receiver is properlyoperating, the resultant signal from the AFC mixer should be at the lFfrequency. The mixed signal is applied to the AFC circuit 246 whichcontains discriminator and reference oscillator circuitry to generate aDC signal for control of the local oscillator 224. If it is impossibleto drive oscillator 224 to the desired frequency value, the resultingsignal is applied to the gate 222 and gate 206 in order to actuate afail indicator light 254 located on the aircraft instrument panel.Additionally, the presence of minimum transmitter peak output power issensed by the power monitor circuit 204, and the fail indicator light254 is energized if the output power falls below a predetermined minimumvalue.

The presence of mixer crystal bias current is also determined by thegate 222 and the fail indicator light 254 is illuminated if a currentfailure occurs. The illumination of the fail indicator light 254indicates a condition below design minimums, but does not necessarilyindicate a complete failure of the radar. Operator adjustment will berequired to judge when the information displayed by the system hasdeteriorated to a point of being completely unusable. To enable theoperator to make such a decision, the movable switch arm 248 may bemoved to the manual AFC test position and a movable switch arm 256 movedto connect the output of the linear amplifier 228 with a ringing line258.

The ringing line 258 generates a series of IF pulses spaced apredetermined delay apart, the pulses being fed through the amplifier232 for display upon the visual indication system of the invention. Sixhorizontal lines are displayed upon the radarscope, along with onevertical line at a position equivalent to the aircraft line of flight.This is accomplished by simulating an altitude input of 500 feet intothe display. The ringing line 258 is actuated by an attenuatedtransmitter pulse which excites the ringing line to create a pulse trainof 60 MHz pulses which are 2,000 feet apart in radar range and whichdecrease in amplitude with increasing range. The pulse trains producedby the ringing line 258 are displayed on the visual display ashorizontal lines to give an indication of correct operation of theantenna scan drive circuitry, the synchros and the display circuitry.

The amplitude of the injected pulses into the amplifier 232 is such thatthe six horizontal lines will be produced on the radarscope equivalentto two, four, eight, ten and twelve thousand feet ranges as viewed from500 feet. The seventh and subsequent pulses from the ringing line 258will fall below the system threshold and will thus not be displayed. Theline display provided by the ringing line gives a good indication ofproper receiver gain control setting, and if less than six lines aredisplayed when the system is put in the test position, the receiversensitivity is below operating minimums. The vertical strobe whichappears on the face of the visual display in the test mode is positionedv by the antenna position synchro. The position of the vertical strobehorizontally relative to the center line is a measure of the linearityand accuracy of the display sweeps in the bore site position.

For additional description of radar receiver operation, reference ismade to Introduction To Radar Systems, Chapter 8, by Merrill l. Skolnik,1962, Mc- Graw-Hill.

RADAR TRANSMITTER FIG. 11 illustrates a block diagram of the presentradar transmitter. Input power is supplied to the present system via the400 cps conventional aircraft supply and passed through a line filteringsystem which filters out the high frequency components of the aircraftvoltage supply system. Three-phase relay switch 282 switches the 400cycle cps signal into a plate transformer 284. Overload protectorcircuit 286 prevents overload of the system and a magnetron filamentrelay circuit 288 supplies current to the magnetron filament. Current issupplied to the filament of the thyratron of the circuit via atransformer 290.

A three-phase bridge 292 supplies rectified voltage via the L-sectionfilter 294 to a charging choke 296. A bleeder circuit 298 providesdischarge protection to the filter 294 when the system is turned off.The charging choke 296 includes inductors which provide a high impedanceload for the system. The voltage is applied via an inverse and chargingdiode assembly 300 to the transmitter thyratron 302. A trigger module304 supplies trigger pulses to the grid of the thyratron 302. The outputof the thyratron 302 is applied through a pulse forming network 306which pulses when the thyratron 302 fires. The pulses from the network306 are applied through a pulse transformer 308 which supplies pulses tothe magnetron 310. The modulator of the invention is oil filled in orderto eliminate voltage breakdown at high altitudes and to comply withdecompression tests required to meet FAA environmental specifications.While a number of Ka band magnetrons are commer cially available, thepreferred embodiment of this system utilizes a L-4564 tunable tubemanufactured and sold by Litton Industries which is modified to deliverKW peak power. Power for the magnetron 310 is applied through a filamenttransformer 312. The output of the magnetron 310 is applied to thecirculator 52. r

The synchronizer 58 supplies the PMT signal for timing operations of thesystem in the manner previously described.

In operation of the radar transmitter, the synchronizer 58'supplies aPMT signal to the trigger module 304 which delays the PMT to provide thethyratron trigger signal. The thyratron 302 normally has a highimpedance and the pulse forming network 306, which preferably comprisesa chain of L-C networks, is charged up to the plate voltage applied tothe thyratron 302. When the thyratron is fired, the pulse formingnetwork 306 discharges through the pulse transformer 308 which steps upthe voltage to provide a high voltage drive to the magnetron 310. A 40ns pulse width signal is generated by the pulse forming network 306 forapplication to the magnetron 310. The inverse diode assembly 300supplies a current return path for the energy which is not transferredto the magnetron due to mismatch between the pulse forming network

1. An independent aircraft monitor system comprising: an antennamountable in said aircraft and having a radiation pattern sufficient inthe elevation for detection of an airport, said antenna having a narrowradiation pattern in the azimuth to provide high resolution, means forsweeping said antenna over an angle in the azimuth sufficient fordetection of an airport, radar transmitter and receiver means fortransmitting and receiving radar signals through said antenna, thereceived radar signals being related to a visual indication of saidairport, and means responsive to said radar receiver signals fordisplaying said visual indication of the approaching airport inreal-world linear perspective.
 1. An independent aircraft monitor systemcomprising: an antenna mountable in said aircraft and having a radiationpattern sufficient in the elevation for detection of an airport, saidantenna having a narrow radiation pattern in the azimuth to provide highresolution, means for sweeping said antenna over an angle in the azimuthsufficient for detection of an airport, radar transmitter and receivermeans for transmitting and receiving radar signals through said antenna,the received radar signals being related to a visual indication of saidairport, and means responsive to said radar receiver signals fordisplaying said visual indication of the approaching airport inreal-world linear perspective.
 2. The monitor system of claim 1 whereinsaid means for displaying comprises: a radar scope.
 3. The monitorsystem of claim 1 wherein said antenna radiation pattern in theelevation has an angle of approximately 17*.
 4. The monitor system ofclaim 1 wherein said antenna radiation pattern in the azimuth has anangle of less than 1*.
 5. The monitor system of claim 1 wherein saidantenna is swept over an angle in the azimuth of approximately 30* andsaid radar signals have frequencies in the Ka-band.
 6. The monitorsystem of claim 1 wherein said antenna comprises: an elongatededge-slotted waveguide array mounted horizontally in said aircraft abouta central vertical pivot, and means for mechanically oscillating saidantenna about said vertical pivot.
 7. The monitor of claim 1 whereinsaid means for displaying comprises: a radar scope having horizontal andvertical sweep means, means for controlling said horizontal sweep meansin direct relation to the azimuth position of said antenna, and meansfor controlling said vertical sweep means in accordance with theaircraft altitude and the instantaneous target range of said radarsignals.
 8. The monitor of claim 7 wherein the elevation angle displayedby said vertical sweep means on said radar scope is proportional to theratio of the aircraft altitude and the instantaneous range of said radarsignals.
 9. The monitor of claim 1 and further comprising: range trackermeans in said aircraft and responsive to radar return signals reflectedfrom pseudorandomly coded reflectors adjacent the runway to generaterange to touchdown signals for display.
 10. The monitor of claim 9 andfurther comprising: glideslope detection means responsive to said rangetracker means and responsive to reflected radar signals from reflectorslocated adjacent the runway to generate indications of the aircraft''sposition relative to the desired glideslope.
 11. An aircraft landingmonitor comprising: an antenna mounted in an aircraft and operable totransmit and receive radar signals for detection of an airport, radartransmitting and receiving circuitry for transmitting and receivingradar signals via said antenna, the received radar signals being relatedto a visual indication of said airport, and display means responsive tosaid received radar signals for visually presenting a display of theapproaching airport which corresponds to the real-world perspective viewof the airport from the aircraft.
 12. The aircraft landing monitor ofclaim 11 wherein said display means presents a visual airport runwayindication with a straight forward runway edge having straight linerunway edges converging toward the rear runway edge according toreal-world linear perspective.
 13. The aircraft landing monitor of claim12 wherein said display means continuously presents an indication ofdesired aircraft touchdown on the runway during the landing of theaircraft.
 14. The aircraft landing monitor of claim 12 and furthercomprising: a radar scope having horizontal and vertical sweep means,means for controlling said horizontal sweep means in direct relation tothe azimuth position of said antenna, and means for controlling saidvertical sweep means in accordance with the aircraft altitude and theinstantanEous target range of said radar signals.
 15. The aircraftlanding monitor of claim 14 wherein the elevation angle displayed bysaid vertical sweep means on said radar scope is proportional to theratio of the aircraft altitude and the instantaneous target range ofsaid radar signals.
 16. The aircraft landing monitor of claim 12 whereinsaid display means visually indicates the lateral offset of the aircraftfrom the runway center line.
 17. The aircraft landing monitor of claim12 wherein said display means visually indicates the angular position ofthe aircraft with respect to the airport runway in the roll axis. 18.The aircraft landing monitor of claim 12 and further comprising: meansfor switching said display means for selectively presenting PPI and Bsweep radar displays.
 19. An aircraft landing monitor comprising: anantenna having an elongated housing pivotally mounted for horizontalmovement in the forward portion of an aircraft, said housing supportinga traveling wave edge-slotted waveguide array mounted in an elongatedreflector for directing an antenna radiation pattern narrower in theazimuth than in the elevation, a motor mounted to oscillate said housingto thereby sweep over an azimuth angle sufficient for airport detectionduring approach, radar transmitter and receiver means for transmittingand receiving radar signals via said antenna, the received radar signalsbeing related to a visual indication of said airport, and a radar scoperesponsive to said receiver signals for visually displaying anapproaching airport in real-world linear perspective, said radar scopeincluding means for controlling the sweep thereof in accordance with theaircraft altitude and range of said radar signals.
 20. The landingmonitor of claim 19 and further comprising: means for continuouslysensing the position of said antenna, and means operable in response tothe sensed antenna position for driving said motor to maintain thepredetermined oscillation of said antenna.
 21. The landing monitor ofclaim 19 wherein said means for controlling comprises: means fornonlinearly driving the vertical sweep of said radar scope to generate avisual display of a straight forward runway edge with straight runwayedges converging toward a rear runway edge according to real-worldlinear perspective.